A powertrain of a vehicle includes an engine, a torque converter, and a transmission coupled in series. If the engine is an internal-combustion engine, the engine contains cylinders that serve as combustion chambers that convert fuel to rotational kinetic energy. The torque converter transmits rotational motion from the engine to the transmission while allowing slippage between the engine and transmission, for example, while the engine is running and the vehicle is stopped. The transmission transmits the kinetic energy from the torque converter to a drive axle and ultimately to wheels of the vehicle, while applying a gear ratio allowing different tradeoffs between torque and rotational speed.
Noise, vibration, and harshness (NVH) constraints can limit the fuel economy possible for the powertrain. Deactivating cylinders of the engine can increase the efficiency of the engine, but running the engine with fewer cylinders can cause torque pulsations that are unpleasant for occupants of the vehicle. Likewise, reduced slippage in the torque converter can increase the efficiency of the powertrain, but reduced slippage also transmits more vibrational shocks from the engine to occupants. And finally, reducing the vehicle speeds at which gear shifts occur or gear ratios change can increase fuel economy but may also increase the noise and vibrations experienced by occupants.